Abstract:

Alginate-medium-resazurin-diatomaceous silica microspheres (AMRD microspheres) were prepared to establish
a rapid method for counting the number of bacterial cells. The results suggested that the positive optimum linear correlation
between the concentration of bacterial cells and discoloration time of AMRD microcapsules was achieved at a ratio of
alginate to diatomaceous silica of 1:1.4 with single medium concentration. The limit of detection (LOD) of the method was
2.02×102 CFU/mL. The detection time was 2–16.5 h. The detection sensitivities for Escherichia coli and Staphylococcus
aureus were 1.62 × 103 CFU/mL and 2.03 × 103 CFU/mL, respectively. The adsorption isotherms could be described
by the Freundlich equation and the coefficient of adsorption (1/n) was 0.5–1.0, which was thus considered as moderate
adsorption. No significant change in the adsorption capacity was observed at varying temperatures at a low bacterial cell
concentration and the time needed to reach the maximum bacterial adsorption balance was 30–45 min. In conclusion, AMRD
microcapsules is a new rapid and economical bacterial cell counting method, which can be applied in the fields of food,
water source and environmental monitoring.

Key words: alginate, diatomaceous silica, resazurin, bacterial cell counting, adsorption for bacteria